1. Field of the Invention
The present invention relates to a digital predistortion linearizer applicable to millimeter-wave band point-to-point communications.
2. Description of the Related Art
Current communication systems have been developed in a way that more and more information is transmitted. In order to improve spectral efficiency, digital modulation systems have become much more complicated than the past. A simple on-off keying (OOK) modulation that has been conventionally applied to millimeter-wave point-to-point communication systems has been developed to a high spectral efficiency modulation such as quadrature phase shift keying (QPSK), 8-phase shift keying (8PSK), 16-quadrature amplitude modulation (16QAM), etc.
However, in the high spectral efficiency modulation, a ratio between a maximum power and an average power of a transmission signal is greater than 10 dB. Thus, in order to transmit a signal without distortion, a transmission power amplifier at a front-end of an antenna is required to have a power greater than a desired level.
To decrease the ratio between the maximum power and the average power of the transmission signal, a method of reducing distortion of a signal by reducing the maximum power of the transmission power amplifier and using a linearization circuit has been mainly used.
The linearization of a power amplifier may include a method of using a feedback circuit, a feed forward method including extracting an out-of-phase component of generated distortion, amplifying the out-of-phase component using a sub-amplifier, and coupling the amplified component with a signal output from a main-amplifier to offset the distortion, and a predistortion linearization including pre-generating a distortion signal, applying the distortion signal to an input signal, and offsetting the distortion in an amplifier while the signal passes through the amplifier.